What I think is causing the confusion here is the term "flat-footed". Just because the players heels touch the ground does not make him non-athletic in his postion. For those catchers that say they are more balanced and more athletic I would ask if they hit with a stance up on the balls of their feet, we their heels lifted off the ground?
I suspect they do not hit up on the balls of their feet. It would not be a very balanced postion to hit in. For the same reason catching on the balls of the feet is not very balanced either.
Catcher's that want a solid base, one that allows them to move left to right, should always be set up with their toes pointed up the baselines and their heels in contact with the ground. Not sitting back on their heels, but in contact woith the ground at all times.
I have added some pics in a photo album online that show catchers in trheir receiving positions as I have described. One of the pictures shows a 10 yr old catcher in a very nice man-on pic. Thighs flat to the ground. Weight well balanced. The other 2 pics are of a very good fastpitch receiver and the last one is my oldest son from a clinic he and I just did.
Any questions let me know
http://pg.photos.yahoo.com/ph/catchingcamp/my_photos